WARNING: The following contains spoilers for the back-up story "Secret Meetings" from Batman #122, on sale now from DC Comics.
Slade Wilson may be in the middle of a bitter battle between Batman and Damian Wayne's Robin right now, but Deathstroke's greatest rivalry will always be with the original Boy Wonder - Dick Grayson. This bitter feud began with the Teen Titans, stretching all the way back to the Judas Contract storyline. Or at least, that's what we thought.
The bitter rivalry actually began many years before Slade took the Teen Titans contract, as revealed in the Batman #122 backup story "Secret Meetings" (by Joshua Williamson, Trevor Hairsine, Rain Beredo, and Willie Schubert). In this latest tale, which takes place just as the Dark Knight adopted Robin as his crime-fighting partner, someone put a hit out on the Boy Wonder. This was a job for one of the greatest assassins in the DC Universe but it has changed everything.
Deathstroke took the contract on Robin and, whilst Batman stopped him before he could even fire a shot, it adds a whole new element to this long and bitter history. It was thought that the first time Slade encountered Robin was alongside the Teen Titans and that the basis for animosity towards the crime fighter came from that team.
Originally, Slade's son, Grant Wilson, took a contract on the Titans but died before he could fulfill it. Although this was due to enhancements given to him by H.I.V.E., Slade nevertheless blamed the Titans for his son's death. Deathstroke adopted his son's unfinished contract, which became the fateful "Judas Contract". Not only was this the biggest betrayal in Titans history, after Slade planted Terra on the team, but the story was also Dick Grayson's debut as Nightwing. Therefore, their fearsome relationship will always be connected to Dick's debut as his own hero.
The rivalry only grew as the years went on, especially around the time of the Infinite Crisis. When Grayson attempted to infiltrate the Secret Society of Supervillains, he trained Slade's daughter Rose and taught her to be a hero. Although an agreement that was struck between the two had Grayson stop teaching Rose if Slade stayed out of Blüdhaven, Deathstroke went back on the deal and destroyed Nightwing's home city in the Crisis event anyway. If that wasn't bad enough, he was also hired by Talia al Ghul not long after to kill Dick when he was Batman - by taking control of his Robin, Damian Wayne. Is it any wonder their feud has endured for so many years?
Although Dick doesn't know it, as Batman stepped in, this is his and Slade's first encounter. It might explain why Deathstroke took things so personally for all these years, going so far as to destroy Blüdhaven and take control of Damian. Even if both of those were contracts, there are plenty of others he could have accepted instead. Slade blames the Titans for his son Grant's death and that's why he hates them but there was always something else to his hatred for Dick Grayson. Finding out that he failed a hit on the Boy Wonder twice, both with the Titans and earlier here in Gotham, suddenly the intensity of this rivalry makes more sense. It goes beyond the Titans because it has always gone beyond the Titans.
This backup story adds a whole new dimension to their decades-long feud. Deathstroke has a reputation for fulfilling his contracts and only a rare few have gone unfulfilled. The contract on the Teen Titans was one of them and look how that went - they've been one of the villain's biggest targets for years. So, the fact that the contract on Dick Grayson has been eating away at him all this time, since he first became Robin, explains why Slade Wilson has wanted to hurt him worse than he's wanted to hurt anyone else.